As is known, apparatus for extracorporeal blood treatment typically comprise at least a blood removal line from the patient, at least a treatment unit where the blood removed from the patient is sent, and at least a return line for the treated blood to the patient. According to the types of treatment to be performed, the treatment unit may comprise an ultrafilter, a plasma filter, a hemofilter, a hemodiafilter, or another treatment unit. With the aim of connecting the blood removal line and the blood return line with the cardiovascular system of the patient, vascular access organs are used, such as for example needles, catheters, cannulas or other organs besides, which suitably inserted in a blood vessel that is a part of the cardiovascular system of the patient, enable removal of the blood to be treated and the return of the treated blood to the patient.
For example a first access organ may be terminally connected to the blood removal channel from the patient, and a second access organ may be connected to the blood return line to the patient: these access organs are inserted into the patient's cardiovascular system, for example at a fistula, and thus they enable removal of the blood and return of the blood to the patient.
It is clear that in the described system a double access must be made on the patient, one for the first access organ and one for the second access organ. As some patients have difficulty in contemporaneously receiving two access organs, processes and apparatus have been developed which use extracorporeal circuits having a single access to the patient: in this case, the single access is used both for removing the blood to be treated and for returning the treated blood to the patient. As the same vascular access is used for the double function of removing and returning the blood, the access organ is suitably connected with the extracorporeal circuit: further, the control of the removal and the return of the blood are coordinated according to temporally alternated stages.
A known technical solution described in U.S. Pat. No. 4,599,165 comprises using the extracorporeal circuit in a single access configuration; in this solution a dialysis apparatus is provided, in which the extracorporeal circuit exhibits a single needle and a first blood pump is predisposed to operate on the blood removal line from the patient, while a second blood pump is predisposed to return the blood to the patient and operates on the return line located downstream of the blood treatment unit which, in the example, comprises a hemodialyzer. The two pumps are active alternatively such that in a first stage there is blood removal into the extracorporeal circuit and in a second stage there is return of the blood to the patient.
In the apparatus operating with a single vascular access, when the user passes from the single-access mode to the double-access mode (in which an access is dedicated to the blood removal line and another to the blood return line) a problem arises linked to the pump present on the blood return line to the patient, as in the double-access mode the removal and return of the blood have to be done contemporaneously. In this regard, it is worthy of note that the pumps used in extracorporeal blood circuits are mostly occlusive pumps, for example peristaltic pumps, that when not moved prevent passage of fluid through the tract of tube on which the pumps operate. Should it be desired to pass from a single-access operating mode to a double-access operating mode, the situation would arise in which when the first pump located on the blood removal line is in operation, the second pump constitutes, in effect, an obstacle to the return of the treated blood to the patient.
Likewise, if the second pump were to be in operation, the first pump would constitute an obstacle to the aspiration of the blood from the patient. With the aim of obviating this type of drawback, the extracorporeal blood treatment systems in use at present comprise using exclusively the blood pump located on the blood removal line from the patient and controlling the motion thereof according to a predetermined revolution rate set by the operator or deduced by the machine on the basis of the blood flow rate desired by the operator. Vice versa, the pump located on the blood return branch to the patient is manually disengaged from the respective tube segment, such that the intervention of the pump is excluded and thus the tube segment is completely free of the occlusive action of the pump. Although the above-described solution has been adopted in the past, it exhibits some drawbacks.
Firstly, the passage from a single vascular-access mode towards a double vascular-access mode involves manual intervention by an operator who has to disengage the pump from the respective tract of tube. Consequently, should the operator not intervene by timely disengaging the tract of tube associated to the second pump, there would inevitably ensue a situation in which the pump would occlude the respective tract of tube during the treatment, thus causing interruption of the treatment itself with a consequent machine halt. Further, even should an operator intervene adequately, it is clear that the above-described procedure leads to an intervention on the part of the operator, with a consequent impossibility of automating the process and slowness in the performing of the passage from single-vascular-access to double-vascular-access.